Valve mechanism for internal combustion engines

ABSTRACT

A valve operating device for an internal combustion engine is capable of increasing a negative valve overlapping duration when maximum lift amounts of an intake valve and an exhaust valve are small. The valve operating device is provided with intake-side and exhaust-side characteristic adjustment mechanisms for adjusting operating characteristics of an intake valve and an exhaust valve. Each characteristic adjustment mechanism has a control cam rotating integrally with a cam shaft, an electric motor that causes a holder pivoted on the cam shaft to rotate about the cam shaft, a sub-rocker lever pivoted on the holder and caused to oscillate by the control cam, and a valve cam that is caused to oscillate around the cam shaft by oscillation of the holder and the sub-rocker lever, for causing oscillation of main rocker levers. The electric motor causes the holder to oscillate in such a manner that the valve open timing of the intake valve is retarded as a maximum lift amount of the intake valve becomes smaller and the valve close timing of the exhaust valve is advanced as a maximum lift amount of the exhaust valve becomes smaller.

TECHNICAL FIELD

The present invention relates to valve operating device for opening andclosing operation of an intake valve and an exhaust valve of an internalcombustion engine, and in more detail, relates to a valve operatingdevice provided with characteristic adjustment mechanisms for adjustingvalve open timing of an intake valve and valve close timing of anexhaust valve at the same time as adjusting a maximum lift amount of theintake valve and the exhaust valve.

BACKGROUND ART

A valve operating device provided with adjustment mechanisms foradjusting a valve open timing of an intake valve and valve close timingof an exhaust valve at the same time as adjusting a maximum lift amountof the intake valve and the exhaust valve is known from the disclosureof JP 2000-3721 A. The valve operating device is provided with aneccentric cam fixed to a drive shaft rotating in response to rotation ofa crankshaft, an annular link rotatably engaged with the outer peripheryof the eccentric cam, a rocker lever which is rotatably engaged with theouter periphery of a control cam that is fixed in an eccentric manner toa control shaft arranged substantially parallel to the drive shaft andwhich is pivoted about the annular link at one end thereof, and arocking cam rotatably engaged with the drive shaft and connected to theother end of the rocker lever via a link.

The rocking cam for opening and closing operations of the intake valveand the exhaust valve oscillates to vary a maximum lift amount and anoperating angle of each of the intake valve and the exhaust valve whenvariation of a distance between the rocking center of the rocker leverand the rotational center of the drive shaft occurs when the controlshaft rotates in accordance with engine driving conditions. The controlshaft is rotationally controlled in such a manner that as the maximumlift amounts of the intake valve and the exhaust valve become smaller,the maximum lift timing is moved towards being retarded at the intakevalve, and moved towards being advanced at the exhaust valve. As aresult, the valve open timing of the intake valve is retarded by anamount that is larger than the amount of advance of the valve closetiming of the intake valve, while the valve close timing of the exhaustvalve is advanced by an amount that is larger than the amount ofretardation of the valve open timing of the exhaust valve, and it isthus possible to improve fuel consumption rate and purify the exhaustgas by using combustion gas retained in the combustion chamber.

On the other hand, SAE TECHNICAL PAPER SERIES, 2000-01-1221, (Mar. 6–9,2000), “Design and Development of a Mechanical Variable Valve ActuationSystem” by Ronald J. Pierik and James F. Burkhard discloses a valveoperating device for an internal combustion engine provided with anadjustment mechanism for advancing valve open timing of the intake valveas the maximum lift amount of the intake valve becomes smaller.

Here, the intake valve is opened and closed by a valve operating deviceprovided with an adjustment mechanism, and the exhaust valve is openedand closed by the valve operating device that is not provided with acharacteristic adjustment mechanism. The adjustment mechanism has aninput cam provided on a cam shaft synchronized with a crankshaft, anoutput cam supported on a cam shaft, a frame pivoted on the cam shaft, alink with one end pivoted on the output cam so as to be capable ofswinging, a rocker lever having a roller coming into contact with theinput cam, and having one end pivoted on the frame and the other endpivoted on the link so as to be capable of swinging, and a control shaftfor causing the frame to oscillate. As the maximum lift amount of theintake vales become smaller, the valve open timing is kept substantiallythe same, while the valve close timing is advanced.

With the valve operating device disclosed in JP 2000-3721 A, a movementangle at the maximum lift timing is determined by an angle through whichthe swinging center of the rocker lever rotates with respect to thecenter of rotation of the drive shaft, when the control cam is rotatedby the control shaft. However, since the rocker lever is rotatablysupported by a control cam fixed to the control shaft positioned awayfrom the drive shaft supporting the rocking cam, the rotational angle ofthe oscillating center of the rocker lever around the rotational axis ofthe drive shaft is dependent on the amount of eccentricity of the rockerlever and is limited to a small value. This means that it is difficultto cause a large amount of combustion gas to be retained in thecombustion chamber by carrying out a large amount of retard of theintake valve open timing and a large amount of advance of the exhaustvalve close timing, thus increasing the duration from the closing of theexhaust valve to the opening of the intake valve during the period fromthe exhaust stroke and to the intake stroke (referred to hereinafter as“negative valve overlaping duration”).

On the other hand, the valve operating device disclosed in “Design andDevelopment of a Mechanical Variable Valve Actuation System” mentionedhereinabove is not provided with a mechanism for adjusting the valveclose timing in the exhaust valve operating device, and it is difficultto retain a sufficient combustion gas in the combustion chamber becausethe intake valve is opened and closed without substantial change in thevalve open timing of the intake valve even if there is a change in themaximum lift amount so that the valve overlapping duration hardlychanges.

The present invention has been made in view of the above describedsituation, and the main object of the invention is to provide a valveoperating device capable of increasing the negative valve overlappingduration when the maximum lift amounts of the intake valve and theexhaust valve are small. The present invention further contemplatesmaking compact a characteristic adjustment mechanism for adjusting eachof the operating characteristics of the intake valve and the exhaustvalve, and also further simplifying the structure thereof and causing adecompression operation by the characteristic adjustment mechanisms.

DISCLOSURE OF THE INVENTION

To attain the above objects, the invention provides a valve operatingdevice for an internal combustion engine, including an intake-side camfollower for contacting an intake valve to open and close the intakevalve, an exhaust-side cam follower for contacting an exhaust valve toopen and close the exhaust valve, and an intake-side characteristicadjustment mechanism and an exhaust-side characteristic adjustmentmechanism for respectively adjusting characteristics of the intake valveand the exhaust valve, wherein each of the characteristic adjustmentmechanisms comprises: a cam shaft that rotates together with rotation ofa crankshaft of the internal combustion engine; a control cam thatrotates together with the camshaft; a holder rotatably supported on thecam shaft; a driving device that causes the holder to oscillate aroundthe cam shaft; a rocker lever rotatably supported on the holder to becaused to oscillate by the control cam; and a drive cam that is causedto rotate around the cam shaft by oscillation of the holder transmittedvia the rocker lever and by oscillation of the rocker lever, to drivethe intake-side cam follower or the exhaust-side cam follower; whereinthe driving device of each of the intake-side characteristic adjustmentmechanism and the exhaust-side characteristic adjustment mechanism isconfigured to cause the associated holder to oscillate in such a mannerthat a valve open timing of the intake valve is retarded as a maximumlift amount of the intake valve becomes smaller and the valve closetiming of the exhaust valve is advanced as a maximum lift amount of theexhaust valve becomes smaller.

In this way, in both the characteristic adjustment mechanisms,rotational angle of the rocker lever around the cam shaft, whichdetermines the advance amount of the intake valve open timing and theretardation amount of the exhaust valve close timing, is made tocoincide with the rotational angle of the holder which is rotatablysupported on the cam shaft on which the valve cam is supported and isoscillated by the driving device. For this reason, it is possible to setan amount of variation of the rotational angle of the rocker leveraround the cam shaft to a large value. Accordingly, it is possible tomake the negative valve overlapping duration large and to significantlyincrease the amount of combustion gas retained in the combustionchamber, namely, the internal EGR amount.

As a result, according to the invention, the following effects areachieved. Specifically, the intake-side characteristic adjustmentmechanism and the exhaust-side characteristic adjustment mechanism, areprovided with the control cam rotating with the cam shaft, the holderrotatably supported on the cam shaft, the driving device for causing theholder to oscillate around the axis of the cam shaft, the rocker leverpivoted on the holder and caused to oscillate by the control cam, andthe valve cam that is caused to oscillate by oscillation of the holderand oscillation of the rocker lever to cause oscillation of theintake-side cam follower or the exhaust-side cam follower. With theseintake-side characteristic adjustment mechanism and the exhaust-sidecharacteristic adjustment mechanism, it is possible to set an adjustmentamount of the rotational angle of the rocker lever around the cam shaftto a large value by causing oscillation of the respective holders aroundthe cam shaft in such a manner that the valve open timing is retarded asthe maximum lift amount of the intake valve becomes smaller and thevalve close timing is advanced as the maximum lift amount of the exhaustvalve becomes smaller. Consequently, it is possible to make the negativevalve overlapping duration large by increasing the amount of advancementof the exhaust valve close timing and the amount of retardation of theintake valve open timing. In this way, it is possible to significantlyincrease the amount of combustion gas retained in the combustionchamber, so that generation of nitroxides is suppressed by thecombustion gas retained in the combustion chamber. Further, vaporizationof the fuel is promoted by heat of the combustion gas in the combustionchamber, so that hydrocarbon (HC) emission is suppressed with resultantimprovement in combustibility, which improves exhaust emissions andreduces pumping loss to improve fuel consumption rate.

In the valve operating device of the present invention, the cam shaftmay be a single common cam shaft and the driving device may be a singlecommon driving device shared by both the intake-side characteristicadjustment mechanism and the exhaust-side characteristic adjustmentmechanism.

In this way, the cam shafts and driving device are used in common by theintake-side and exhaust-side characteristic adjustment mechanisms.

As a result, the following effect is obtained. That is, it is possibleto make the intake-side and exhaust-side characteristic adjustmentmechanisms compact, and it is also possible to simplify the structure ofthe valve operating device with resultant reduction in the costs.

Preferably, the driving device is configured to cause the holder of eachof the intake-side characteristic adjustment mechanism and theexhaust-side characteristic adjustment mechanism to swing to adecompression position to open each of the intake valve and the exhaustvalve by means of the associated drive cam.

In this way, the holder causes oscillation of the valve cam via therocker lever, and the valve cam causes the intake valve and exhaustvalve to open for decompression operation. As a result, the followingeffect is obtained. Since the driving device causes the holders of theintake-side and exhaust-side characteristic adjustment mechanisms tooscillate to decompression open positions to open the intake valve andthe exhaust valve by the respective drive cams during the compressionstroke of the internal combustion engine, in order for the valve camsoscillated by the holders to cause the intake valve and the exhaustvalve to open to decompression positions, it is possible to carry out adecompression operation without separately providing a mechanism forcarrying out the decompression operation.

Preferably, the driving device comprises a reversible motor, a drivingmember driven linearly by the motor, and a link connecting the drivingmember and the holder to each other.

The holder may comprise a pair of plate members supported by the camshaft for oscillation around the cam shaft and disposed in a spaceddisposition with respect to the axial direction of the cam shaft, and asupport shaft connecting the plate members in the axial direction of thecam shaft and forming a pivot shaft for pivotal support of the rockerlever on the holder.

Further, the control cam and the drive cam are preferably supported onthe cam shaft between the plate members.

The rocker lever is preferably pivoted at one end thereof to the holderand at the other end thereof to the drive cam via a link, and the rockerlever may have at an intermediate part thereof a portion to be actedupon by the control cam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a valve operating device of the embodiment of the presentinvention and is a cross sectional view of a cylinder head taken alongIa—Ia line in FIG. 2, partly showing a cross section taken along Ib—Ibline, of the cam shaft holder for an internal combustion engine providedwith the valve operating device;

FIG. 2 is a cross sectional view taken along II—II line on FIG. 1;

FIG. 3 is a front elevational view of a control cam of the valveoperating device of FIG. 1;

FIG. 4A is a front elevational view of a sub-rocker lever, link andvalve cam in a mutually linked state, in an exhaust-side characteristicadjustment mechanism of the valve operating device of FIG. 1;

FIG. 4B is a cross section along B—B line in FIG. 4A;

FIG. 5 is a section taken along V—V line in FIG. 2, of part of anintake-side characteristic adjustment mechanism of the valve operatingdevice of FIG. 1, and shows a state in which the intake valve is openedwith a high lift amount;

FIG. 6 is a view similar to FIG. 5, but showing a state where the intakevalve is opened with a low lift amount;

FIG. 7 is a view similar to FIG. 5, but showing a state where the intakevalve is opened to a decompression opening amount; and

FIG. 8 is a graph showing operating characteristics of an intake valveand an exhaust valve operated by the valve operating device of FIG. 1.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described hereafter withreference to FIG. 1 to FIG. 8.

Referring to FIGS. 1 and 2, an internal combustion engine to which avalve operating device V of the present invention is applied is a SOHCsingle cylinder 4-cycle engine mounted on a small vehicle or amotorcycle. As shown in FIG. 1, the internal combustion engine comprisesa cylinder head 1 coupled to an upper end of a cylinder (not shown inthe figure) having a cylinder bore in which a piston (not shown in thefigure) is fitted for reciprocation therein, and a head cover 2 coupledto an upper end of the cylinder head 1. A combustion chamber 3 is formedin the cylinder head 1 adjacent to the lower surface thereof, and anintake port 4 and an exhaust port 5 are formed to open in the combustionchamber 3.

An intake opening of the intake port 4 and an exhaust opening of theexhaust port 5 are respectively opened and closed by an intake valve 7and an exhaust valve 8, respectively, that are reciprocally supported inthe cylinder head 1 and urged in normally closed positions by respectivevalve springs 6. The intake valve 7 and the exhaust valve 8 are openedand closed by the valve operating device V. This valve operating deviceV, except for an electric motor 30, is arranged inside a valve chamber 9formed by the cylinder head 1 and the head cover 2.

A fuel supply system for supplying liquid fuel into sucked air, and anintake unit provided with an intake tube for leading a thus formedmixture of fuel and air to the intake port 4, are attached to one sidesurface 1 a of the cylinder head 1 where an inlet of the intake port 4opens out. Also, an exhaust unit provided with an exhaust pipe forleading combustion gas flowing from the combustion chamber through theexhaust port 5 to the outside of the internal combustion engine isattached to the other side surface 1 b of the cylinder head 1 where anoutlet of the exhaust port 5 opens out.

A mixture sucked into the combustion chamber 3 from the intake port 4 inthe intake stroke in which the intake valve 7 is opened and the pistonis lowered, is compressed by the piston rising in the compressionstroke. The mixture is thereafter ignited by a spark plug (not shown) toachieve combustion. The piston that is lowered by the pressure of thecombusted gas in the expansion stroke then drives the crankshaft inrotatation via a connecting rod. The combustion gas is discharged to theexhaust port 5 from the combustion chamber 3 as exhaust gas in theexhaust stroke.

The valve operating device V comprises an intake-side main rocker lever10 as an intake side cam follower for abutting contact with a tip end ofa valve stem 7 a of the intake valve 7 that opens and closes the intakevalve 7, and an exhaust-side main rocker lever 11 as an exhaust side camfollower for abutting contact with a tip end of a valve stem 8 a of theexhaust valve 8 that opens and closes the exhaust valve 8. As shown inFIG. 2, the valve operating device V further comprises an intake-sidecharacteristic adjustment mechanism Mi and an exhaust-sidecharacteristic adjustment mechanism Me for adjusting operationalcharacteristics of the intake valve 7 and the exhaust valve 8, thesecharacteristics here being lift amount and valve opening and closingtimings.

The intake-side main rocker lever 10 is supported at a central supportsection 10 a thereof for oscillation on a rocker shaft 12 fixed to astationary cam shaft holder H. The intake-side main rocker lever 10 hasat one end thereof an operating section 10 b for abutting contact withthe valve stem 7 a and at the other end therof a roller 10 c (FIG. 5)that is in rolling contact with a valve operating cam 18. The roller 10c acts as a contact part with the valve operating cam 18 which will bedescribed later. The exhaust-side main rocker lever 11 is supported at acentral support section 11 a thereof for oscillation on another rockershaft 12 fixed to the stationary cam shaft holder H. The exhaust-sidemain rocker lever 11 has at one end thereof an operating section 11 bfor abutting contact with the valve stem 8 a and at the other end therofa roller 11 c that is in rolling contact with a valve operating cam 18.The roller 11 c acts as a contact part with the valve operating cam 18.

The intake-side characteristic adjustment mechanism Mi and theexhaust-side characteristic adjustment mechanism Me have basically thesame construction. Therefore, description will be made mainly of theintake-side characteristic adjustment mechanism Mi, and, when required,members relating to the exhaust-side characteristic adjustment mechanismMe will be mentioned in brackets.

Referring to FIG. 5 as well, the intake-side characteristic adjustmentmechanism Mi comprises a single cam shaft 13 shared by the exhaust-sidecharacteristic adjustment mechanism Me, a control cam 14 rotatingtogether with the cam shaft 13, a holder 15 rotatably supported on thecam shaft 13, a driving device D (FIGS. 1 and 2) fixed to the head cover2 for causing oscillation of the holder 15 about the cam shaft 13, asub-rocker lever 16 pivoted to the holder 15 and caused to oscillate bythe control cam 14, a link 17 connected at one end thereof to thesub-rocker lever 16 so as to be able to swing, the afore-mentioned valvecam 18 rotatably supported on the cam shaft 13 and connected to theother end of the link 17 so as to be able to swing, and a spring 19constituted by a torsion coil spring as an urging member for urging thesub-rocker lever 16 so as to contact the control cam 14.

When the holder 15 is not oscillated with respect to the cam shaft 13,the valve cam 18 is caused to oscillate around the cam shaft 13 byoscillation of the sub-rocker lever 16 transmitted via the link 17, tocause oscillation of the intake-side main rocker lever 10 (exhaust-sidemain rocker lever 11) thus causing opening and closing operation of theintake valve 7 (exhaust valve 8). When the holder 15 is caused tooscillate by the driving device D, the valve cam 18 is caused tooscillate around the camshaft 13 by oscillation of the holder 15transmitted via the sub-rocker lever 16 and the link 17.

As shown in FIG. 2, the cam shaft 13 is rotatably supported in thecylinder head 1 by being held in the cylinder head 1 and the cam shaftholder H connected to the cylinder head 1 by means of a bearing 20constituted by ball bearings arranged on both ends of the cam shaft 13,and the cam shaft 13 is driven to rotate by rotation of the crankshafttransmitted via a transmission mechanism, in synchronism with half therotational speed of the crankshaft. A cam sprocket 25 integrallyconnected to one end of the cam shaft 13 constitutes the transmissionmechanism together with a drive sprocket provided on the crankshaft anda timing chain wound around these two sprockets.

Referring to FIG. 3, the control cam 14 is fixed to the cam shaft 13 bypress fitting and has a base circular section 14 a defining the camsurface, and a cam lobe section 14 b protruding in a radial directionfrom the base section 14 a. The control cam 14 has an operating anglerange set relative to the crank angle such that the intake valve 7 iscaused to open at least in the intake stroke, the sub-rocker lever 16normally pressed against the cam surface is caused to oscillate, and theoscillated sub-rocker lever 16 causes the valve cam 18 to oscillate viathe link 17.

Referring to FIG. 2, the holder 15 is made up of a pair of first andsecond plates 15 a and 15 b as a pair of support sections separated inthe direction A1 of the rotational axis L1 of the cam shaft 13 (referredto hereinafter as rotational axis direction A1), a bearing 21constituted by ball bearings for supporting the plates 15 a, 15 b so asto oscillate with respect to the cam shaft 13, a cylindrical collar 15 cas a support shaft pivoting the sub-rocker lever 16 as well as definingan interval between the first and second plates 15 a and 15 b in therotational axis direction A1, and a rivet 15 d inserted into the collar15 to rigidly couple the two plates 15 a, 15 b.

A collar 15 e as a support shaft for pivoting a swingable link 36described later is fixed to the first plate 15 a, using a rivet 15 fthat is inserted into the collar 15 e. A pin 15 g for abutting one endof the spring 19 is provided on the second plate 15 b.

Referring to FIGS. 4A and 4B, the sub-rocker lever 16 has a roller 16 aprovided at a middle part thereof as a contact section for contactingthe control cam 14, i.e., it comes into rolling contact with the controlcam 14. The sub-rocker lever 16 also has a supported section 16 b at oneend that is supported on the collar 15 c for oscillation, and aconnecting section 16 c at the other end pivoted on a link pin 22 fixedto one end of the link 17. Therefore, the sub-rocker lever 16 isoscillated with the collar 15 c as an oscillation center by rotation ofthe control cam 14.

A pin 16 d is provided on the sub-rocker lever 16 for abutting with theother end of the spring 19 that is arranged around the outer peripheryof the collar 15 c. The roller 16 a of the sub-rocker lever 16 is thennormally pressed against the control cam 14 by the spring 19, andvibration of the sub-rocker lever 16 due to inertial forces acting onthe sub-rocker lever 16, link 17 and valve cam 18 is prevented.

As shown in FIG. 2, the link 17 is disposed adjacent to the control cam14 with respect to the rotational axis direction A1 and a link pin 23(FIGS. 4A and 4B) is fixed to the other end of the link 17, and thevalve cam 18 is pivoted swingably on the link pin 23 through a bearing24 in the form of a needle bearing. As shown in FIG. 4A, the valve cam18 has an annular holding section 18 a for holding the bearing 24 and alink connecting section 18 b for pivotal connection to the link 17through a pin 23.

A cam surface S is formed on a part of the outer peripheral surface ofthe annular holding section 18 a. This cam surface S is defined by abase section 18 c for keeping the intake valve 7 (exhaust valve 8) in aclosed state, and a cam land section 18 d continuing from the basesection 18 c and projecting outwards in a radial direction. The cam landsection 18 d is for causing the intake valve 7 (exhaust valve 8) to openvia the intake-side main rocker lever 10 (exhaust-side main rocker lever11) and has such a shape that the lift amount of the intake valve 7(exhaust valve 8) becomes gradually larger in the rotational direction Rof the cam shaft 13.

Therefore, when the rotational positions of the holder 15 around the camshaft 13 or the control cam 14 and of the sub-rocker lever 16 are notchanged in the rotational direction R of the cam shaft 13 (refer to FIG.5), the valve open duration of the intake valve 7 (exhaust valve 8) isshortened and the maximum lift amount is reduced, as the valve cam 18rotates in the rotational direction R of the cam shaft 13.

Then, as shown in FIG. 2, with the holder 15, control cam 14, sub-rockerlever 16, link 17 and valve cam 18 attached to the cam shaft 13, thecontrol cam 14, sub-rocker lever 16, link 17, spring 19 and valve cam 18are arranged between the first and second plates 15 a and 15 b in therotational axis direction A1.

Referring to FIG. 1 and FIG. 2, the single driving device D shared bythe intake-side characteristic adjustment mechanism Mi and theexhaust-side characteristic adjustment mechanism Me includes an electricmotor 30 as an actuator, capable of rotation in the reverse direction,fixed to the outer surface of the head cover 2, a drive rod 32 as adrive member driven by the electric motor 30, and a transmissionmechanism 31 for transmitting rotation of the electric motor 30 to thedrive rod 32. The transmission mechanism 31 is arranged inside the valvechamber 9 and is made up of a worm 31 a rotationally driven by arotating shaft 30 a of the electric motor 30 extending inside the valvechamber 9 through the head cover 2, and a worm wheel 31 b meshing withthe worm 31 a.

A feed screw mechanism is provide between the worm wheel 31 b and thedrive rod 32, as a motion translator for translating rotational movementof the worm wheel 31 b to linear reciprocal motion of the drive rod 32.In order to configure this feed screw mechanism, a female screw section31 c is formed in the inner surface of the worm wheel 31 b, and a malescrew section 32 c for screw engagement with the female screw section 31c is formed on the outer surface of the drive rod 32. The worm wheel 31b is rotatably supported on the cam shaft holder H by way of a bearing33, being a ball bearing, and the drive rod 32 passes through a throughhole 34 formed in the cam shaft holder H and is capable of advancing andretreating motion inside the valve chamber 9.

As shown in FIG. 5, a link 36 constituting a transmission mechanism 35for transmitting motion of the drive rod 32 to the holder 15 to causeoscillation of the holder 15 about the cam shaft 13 is provided betweenthe drive rod 32 and the holder 15. The link 36, as describedpreviously, is mounted on the first plate 15 a at one end foroscillating motion, and mounted on the drive rod 32 at the other end soas to be capable of swinging by pivoting on the link pin 37 fixed to thedrive rod 32.

The electric motor 30 is controlled by a controller 50 (FIG. 2) thatreceives input of detection signals from various sensors for detectingengine operating conditions, such as load on the engine, rotationalspeed, crank angle, being the rotational position of the crank shaft,and cam angle, being the rotational position of the cam shaft 13 atstart of the engine, as well as input from a potentiometer 38 (FIG. 1)as a sensor for detecting the operating condition of the electric motor30.

Operating conditions such as the amount of rotation of the electricmotor 30, direction of rotation, rotation timing and stop timing, etc.,are controlled according to engine operating conditions, based on acontrol map in which relationships between engine operating conditionsand operating conditions of the electric motor 30 are set in advance.When the position of the drive rod 32 changes, respective positions ofthe holder 15, the collar 15 c as the swing center of the sub-rockerlever 16, and the valve cam 18 about the cam shaft 13, namely theoscillation positions of the above elements, are changed according tothe engine operating conditions. Actual operating conditions of theelectric motor 30 are detected by means of detection of the amount ofrotation and the direction of rotation of the worm wheel 31 b using apotentiometer 38 having a detection rod 38 a that is driven to rotate bymeshing with the worm wheel 31 b, and a detection signal from thepotentiometer 38 is fed back to the controller 50.

In the control map, the amount of movement of the drive rod 32 that isalso the amount of drive (amount of rotation) of the electric motor 30,and hence the rotational angle α (Refer to FIG. 6 and FIG. 7) is set asindicated in FIG. 8. The rotational angle α is equal to the angle ofrotation of the sub-rocker lever 16 about the oscillation center thereofand to the angle of rotation of the valve cam 18 about the cam shaft 13.This angle of rotation will hereinafter be referred to as “phase controlangle”. As will be seen from FIG. 8, the rotational angle α is set tosuch a value that the intake valve 7, of which a maximum lift amount andthe open and close timings are varied by the intake-side characteristicadjustment mechanism Mi, has its valve open timing continuously retardedwhile the valve close timing is kept constant or almost constant as themaximum lift amount of the intake valve 7 becomes continuously smaller,and that the exhaust valve 8, of which a maximum lift amount and theopen and close timings are varied by the exhaust-side characteristicadjustment mechanism Me, has its valve close timing continuouslyadvanced while the valve open timing is kept constant or almost constantas the maximum lift amount of the exhaust valve 8 becomes continuouslysmaller.

In this control map, the amount of movement of the drive rod 32 is soset that at the time of the compression stroke when starting theinternal combustion engine, the holders 15 of the intake-side andexhaust-side characteristic adjustment mechanisms Mi and Me, and thevalve cam 18, are caused to rotate by the drive rod 32 in the oppositedirection to the rotational direction R (refer to FIG. 5), the cam landsection 18 d of the valve cam 18 is brought into contact with therollers 10 c and 11 c of the intake-side and exhaust-side main rockerlevers 10, 11, and the intake valve 7 and the exhaust valve 8 are openedwith a small amount of decompression opening.

Next, the operation of the embodiment configured as described above willbe described.

For example, in an operating region of the internal combustion enginesuch as a high load operating region where intake amount is large, theintake valve 7 and the exhaust valve 8 are opened with a large maximumlift amount and a long valve open duration, as indicated, for example bythe solid line T1 in FIG. 8, and the valve overlapping duration is alsomade large to enable high output operation.

In an operating region where intake amount is small, such as a low loadoperating region or low speed operating region, as indicated, forexample, by the single dot dashed line T3 and the dotted line T4, themaximum lift amount and the valve open duration for the intake valve 7are reduced, and in order to cause a large amount of combustion gas tobe retained in the combustion chamber 3, the intake-side andexhaust-side characteristic adjustment mechanism Mi and Me operate so asto advance the valve close timing of the exhaust valve 8 and the retardthe valve open timing of the intake valve 7.

A specific example will be given below. Because the intake-sidecharacteristic adjustment mechanism Mi operates at the same time withand in the same way as the exhaust-side characteristic adjustmentmechanism Me, description in the following will be made mainly on theintake-side characteristic adjustment mechanism Mi with reference toFIG. 1, and FIGS. 5–8, and corresponding elements of the exhaust-sidecharacteristic adjustment mechanism Me will be mentioned in bracketswith description of these elements being dispensed with.

Transition is carried out as stated below from a state of theintake-side characteristic adjustment mechanism Mi (exhaust-sidecharacteristic adjustment mechanism Me) in which the intake valve 7(exhaust valve 8) is open with a high lift amount, which is an operatingregion where the intake amount is large as shown in FIG. 5, to a statein which the intake valve 7 (exhaust valve 8) is open with a low liftamount, which is an operating region where the intake amount is small asshown in FIG. 6.

The worm 31 a and worm wheel 31 b are driven to rotate by the electricmotor 30 that is controlled by the controller 50, and the drive rod 32is advanced in the valve chamber 9 by the feed screw mechanism. At thistime, the drive rod 32 rotates the holder 15 about the cam shaft 13 inthe rotational direction R via the link 36, by the phase control angle αset by the control map, and at the same time the sub-rocker lever 16,link 17 and valve cam 18 rotate about the cam shaft 13 in the rotationaldirection R by the same phase control angle α. In this way,corresponding to the range of oscillation of the sub-rocker lever 16caused by the control cam 14 rotating together with the cam shaft 13, anincreased proportion of the cam surface S (refer to FIG. 4A) of thevalve cam 18, within the range in which contact is made with the roller10 c (roller 11 c), is caused to contact the roller 10 c (roller 11 c)at the base section 18 c thereof, and a reduced proportion of the camsurfaces is caused to contact the roller 10 c (roller 11 c) at the camland section 18 d, as compared with an operating region where the intakeamount is large, with the result that the maximum lift amount of theintake valve 7 (exhaust valve 8) is reduced and the valve open durationis shortened.

At this time, since the sub-rocker lever 16 occupies a position where ithas rotated around the control cam 14 in the rotational direction R bythe phase control angle α, the valve open timing (valve close timing) ofthe intake valve 7 (exhaust valve 8) is correspondingly retarded(advanced), while keeping the valve close timing (valve open timing) thesame or almost the same, as compared with an operating region where theintake amount is large.

For this reason, as will be noted from the curves T2, T3 and T4 in FIG.8 in the case where the phase control angle α of the holder 15 in therotational direction R is larger, as the phase control angle α of theholder 15 in the rotational direction R becomes larger, the maximum liftamount of the intake valve 7 and the exhaust valve 8 becomes smaller,the valve open duration is shortened, the valve close timing of theexhaust valve 8 is advanced significantly, and the valve open timing ofthe intake valve 7 is retarded significantly, so that the valveoverlapping duration is shortened, a negative valve overlapping durationP is increased, and a large amount of combustion gas is retained in thecombustion chamber 3.

At the time of the compression stroke at starting of the engine, asshown in FIG. 7, the holder 15 is rotated in the opposite direction tothe rotational direction R, as a result of the electric motor 30 causingthe drive rod 32 to move backwards. Then, the valve cam 18 is rotated inthe opposite direction to the rotational direction R via the sub-rockerlever 16 and the link 17 by the rotating holder 15, the rollers 10 c and11 c of the intake-side and exhaust-side main rocker levers 10 and 11come into contact with the cam land section 18 b, and the intake valve 7and the exhaust valve 8 are opened with a decompression opening. In thisway, compression pressure is lowered and engine starting is made easy.

Effects of the above-described embodiment will now be described.

As stated above, each of the intake-side characteristic adjustmentmechanism Mi and the exhaust-side characteristic adjustment mechanism Meis provided with the control cam 14 rotating integrally with the camshaft 13, the driving device D for causing the holder 15 pivoted on thecam shaft 13 to oscillate around cam shaft 13, the sub-rocker lever 16pivoted on the holder 15 and caused to oscillate by the control cam 14,and the valve cam 18 caused to oscillate by oscillation of the holder 15and oscillation of the sub-rocker lever 16 for operating the intake-sidemain rocker lever 10 or the exhaust-side main rocker lever 11. Further,the intake-side characteristic adjustment mechanism Mi and theexhaust-side characteristic adjustment mechanism Me are configured suchthat the phase control angle α of the sub-rocker lever 16 around the camshaft 13, for determining the amount of retardation of the valve opentiming of the intake valve 7 and the amount of advancement of the valveclose timing of the exhaust valve 8, is made to coincide with the phasecontrol angle α of the holder 15 that is pivoted on the cam shaft 13supporting the valve cam 18 and caused to oscillate by the drivingdevice D. As a result, the phase control angle α can be set to have alarge variable amount. Therefore, by increasing the amount ofadvancement of the valve close timing of the exhaust valve 8 and theamount of advancement of the valve open timing of the intake valve 7,the negative valve overlapping duration can be made longer. As a result,it is possible to make the amount of combustion gas retained in thecombustion chamber 3, i.e., the internal EGR amount, significantlylarge. Consequently, the combustion temperature is lowered by thecombustion gas retained in the combustion chamber 3 so as to suppressthe generation of nitroxides. Further, vaporization of the fuel ispromoted using heat of the retained combustion gas, combustibility isimproved together with suppression of hydrocarbon (HC) discharge,exhaust emissions are improved, and pumping loss is reduced to improvefuel consumption rate.

In the intake-side characteristic adjustment mechanism Mi and theexhaust-side characteristic adjustment mechanism Me, the cam shaft 13 isa single common cam shaft, and the driving device D is a single commondriving device, which means that the cam shaft 13 and the driving deviceD are shared by both the intake-side and exhaust-side characteristicadjustment mechanisms Mi and Me, so that it is possible to make compactthe intake-side and exhaust-side characteristic adjustment mechanisms Miand Me, and to make the entire structure simple with reduction of thecosts.

At the compression stroke of the internal combustion engine, the driverod 32 driven and moved by the electric motor 30 causes the holders 15of the intake-side and exhaust-side characteristic adjustment mechanismsMi and Me to oscillate to decompression positions in which the intakevalve 7 and the exhaust valve 8 are opened by the respective valve cams18, and in this way the valve cams 18 that are caused to operate by theholders 15 open the intake valve 7 and the exhaust valve 8 atdecompression opening amounts, making it possible to carry out adecompression operation without separately providing a mechanism forcarrying out the decompression operation.

In the following, description will be given for modified structureswhere part of the structure of the above-described embodiment ischanged.

In the above described embodiment, the cam follower is a rocker lever,but the cam follower may also be a lifter or a swing arm. Also, the camshaft can be replaced by a pair of cam shafts, being an intake-side camshaft and an exhaust-side camshaft, and it is possible for the drivingdevice to be provided for each of the intake-side and exhaust-sidecharacteristic adjustment mechanisms Mi and Me.

The internal combustion engine of the above-described embodiment is of asingle cylinder type, but multiple cylinders could also be provided, inwhich case the intake-side and exhaust-side characteristic adjustmentmechanisms Mi and Me sharing a single driving device are provided foreach cylinder.

1. A valve operating device for an internal combustion engine, includingan intake-side cam follower for contacting an intake valve to open andclose the intake valve, an exhaust-side cam follower for contacting anexhaust valve to open and close the exhaust valve, and an intake-sidecharacteristic adjustment mechanism and an exhaust-side characteristicadjustment mechanism for respectively adjusting characteristics of theintake valve and the exhaust valve, wherein each of the characteristicadjustment mechanisms comprises: a cam shaft that rotates together withrotation of a crankshaft of the internal combustion engine; a controlcam that rotates together with the cam shaft; a holder rotatablysupported on the cam shaft; a driving device that causes the holder tooscillate around the cam shaft; a rocker lever rotatably supported onthe holder to be oscillated by the control cam; and a drive cam that iscaused to rotate around the cam shaft by oscillation of the holdertransmitted via the rocker lever and by oscillation of the rocker lever,to drive the intake-side cam follower or the exhaust-side cam follower;wherein the driving device of each of the intake-side characteristicadjustment mechanism and the exhaust-side characteristic adjustmentmechanism is configured to cause the associated holder to oscillate insuch a manner that a valve open timing of the intake valve is retardedas a maximum lift amount of the intake valve becomes smaller and thevalve close timing of the exhaust valve is advanced as a maximum liftamount of the exhaust valve becomes smaller.
 2. The valve operatingdevice for an internal combustion engine according to claim 1, whereinthe cam shaft is a single common cam shaft and the driving device is asingle common driving device shared by both the intake-sidecharacteristic adjustment mechanism and the exhaust-side characteristicadjustment mechanism.
 3. The valve operating device for an internalcombustion engine according to claim 2, wherein the driving device isconfigured to cause the holder of each of the intake-side characteristicadjustment mechanism and the exhaust-side characteristic adjustmentmechanism to swing to a decompression position to open each of theintake valve and the exhaust valve by means of the associated drive cam.4. The valve operating device for an internal combustion engineaccording to claim 1, wherein the driving device comprises a reversiblemotor, a driving member driven linearly by the motor, and a linkconnecting the driving member and the holder to each other.
 5. The valveoperating device for an internal combustion engine according to claim 1,wherein the holder comprises a pair of plate members supported by thecam shaft for oscillation around the cam shaft and disposed in a spaceddisposition with respect to the axial direction of the cam shaft, and asupport shaft connecting the plate members in the axial direction of thecam shaft and forming a pivot shaft for pivotal support of the rockerlever on the holder.
 6. The valve operating device for an internalcombustion engine according to claim 5, wherein the control cam and thedrive cam are supported on the cam shaft between the plate members. 7.The valve operating device for an internal combustion engine accordingto claim 1, wherein the rocker lever is pivoted at one end thereof tothe holder and at the other end thereof to the drive cam via a link, andthe rocker lever has at an intermediate part thereof a portion to beacted upon by the control cam.
 8. The valve operating device for aninternal combustion engine according to claim 1, wherein the drivingdevice is reversible so as to oscillate the holder in oppositedirections, when the holder is oscillated in one direction the valveopen timing of the intake valve is retarded as the maximum lift amountof the intake valve becomes smaller and the valve close timing of theexhaust valve is advanced as the maximum lift amount of the exhaustvalve becomes smaller, and when the holder is oscillated in the oppositedirection the holder of the corresponding intake-side characteristicadjustment mechanism or the exhaust-side characteristic adjustmentmechanism swings to a decompression position to open the intake valve orthe exhaust valve by means of the associated drive cam.
 9. The valveoperating device for an internal combustion engine according to claim 1,wherein the driving device is a single common driving device shared byboth the intake-side characteristic adjustment mechanism and theexhaust-side characteristic adjustment mechanism.